The invention relates to a throttle body, which has at least one housing, a stub pipe arranged in the housing and accommodating a throttle butterfly, and an actuator, which drives the throttle butterfly.
A throttle body of this kind is known from EP 0 337 099 A2, which describes a device for controlling the power of an internal combustion engine provided for the purpose of driving vehicles. Here, the throttle body has a housing in which a positioning motor designed as an electric motor is arranged. Via transmission elements, such as a reduction gear, the actuator drives a moving element, which is a throttle butterfly for controlling the power of the internal combustion engine. However, the production of the device known from EP 0 337 099 A2 requires a particularly high outlay on production and assembly owing to the large number of parts to be produced and assembled.
In the case of a throttle body with an actuator, heat generated in the actuator during the operation of the actuator can lead to particularly severe heating of the components of the actuator. However, an actuator operated subject to continuous particularly severe heating is generally prone to faults and has a particularly short life. A particularly short life of the actuator, in turn, is associated with a particularly high outlay on the maintenance and repair of the throttle body, leading to extremely high costs for the operation of the throttle body.
The object on which the invention is based is therefore to indicate a throttle body of the above-mentioned type with which the outlay on production and assembly is particularly low while, at the same time, particularly severe heating of the actuator is reliably avoided.
According to the invention, this object is achieved by virtue of the fact that the housing is composed of plastic, and functional elements of the actuator are arranged in the housing and are at least partially surrounded by plastic, the throttle butterfly being surrounded by a heat-conducting stub pipe, a functional element of the actuator and the heat-conducting stub pipe being connected to one another in a heat-conducting manner or being of one-piece design.
The invention starts from the consideration that a throttle body that involves a particularly low outlay on production and assembly should have a particularly small number of parts. The number of parts to be assembled is particularly small if there is no need for a separate housing for the actuator and if it is possible to integrate functional elements of the actuator into the housing of the actuator. At the same time, it should be possible to adapt the housing to the spatial dimensions of the functional elements of the actuator in a particularly simple manner. For this purpose, the housing of the throttle body is manufactured from plastic, the housing of the throttle body being designed both as the housing of the throttle body and as the housing of the actuator.
In this arrangement, particularly severe heating of the actuator is reliably avoided if the heat generated in the actuator can be dissipated from the actuator during the operation of the actuator. However, the plastic housing of the throttle body and of the actuator proves unsuitable as a heat dissipation element since the housing of the throttle body and of the actuator should not heat up to a particularly great extent if the actuator is to function in a particularly reliable manner. The actuator should therefore have connected to it a heat conductor, via which the heat generated in the actuator can be dissipated from the actuator and the housing of the throttle body and of the actuator during the operation of the actuator. An additional component of the throttle body can be dispensed with here if a part that is provided in the throttle body in any case can be used as a heat conductor. For this purpose, a functional element of the actuator is connected in a heat-conducting manner to a stub pipe surrounding the throttle butterfly.
It is advantageous if the functional element of the actuator and the stub pipe are in direct contact with one another at at least one point. This ensures direct heat transfer from the functional element of the actuator to the stub pipe, as a result of which the throttle body has a particularly simple construction that has a particularly low susceptibility to faults. To compensate for inaccuracies of fit and for a particularly pronounced thermal conductivity, the connection between the two elements can be assisted by means of thermally conductive paste, for example.
It is advantageous if the stub pipe is composed essentially of metal. Metal is a particularly good heat conductor, ensuring particularly reliable dissipation of the heat generated in the actuator during the operation of the actuator. It is advantageous here if the stub pipe is composed essentially of aluminum. Components made of aluminum can be manufactured with a high accuracy of fit in a particularly simple manner, and the outlay required for the production of the throttle body is therefore particularly low. Moreover, aluminum is intrinsically particularly light, allowing the weight of the throttle body to be reduced to a particularly low level.
The heat absorbed by the stub pipe during the operation of the actuator is removed from the throttle body by the air flowing through the stub pipe. This is a particularly reliable way of avoiding heating of the actuator during the operation of the actuator.
It is advantageous if the stub pipe and the functional element of the actuator have means by which the stub pipe and the functional element of the actuator can be positioned relative to one another. It is advantageous if the means are domes. The word xe2x80x9cdomesxe2x80x9d is used to denote form-locking joints by means of which a first component can be positioned relative to a second component. By virtue of these means, the outlay required for assembly in the production of the throttle body can be reduced to a particularly low level since the stub pipe and the functional element of the actuator can be connected to one another in a particularly simple manner, this being associated with particularly short assembly times for the throttle body. Moreover, this is a reliable way of avoiding inaccuracies of fit, caused by manufacturing tolerances, when joining the stub pipe and the functional element of the actuator together, and as a result the throttle body takes up a particularly small amount of space.
It is advantageous if the means by which the stub pipe and the functional element of the actuator can be positioned relative to one another can be produced both in one piece with the stub pipe and in one piece with the functional element of the actuator of the throttle body. This simplifies the production of the throttle body since there is no need for the additional process of fitting the respective domes. As an alternative or in addition, the means can be connecting elements, e.g. rivets, nails or screws, which can be secured both on the stub pipe and on the functional element of the actuator. As an alternative or in addition, it is furthermore also possible to make provision for the housing of the actuator and the stub pipe to be pressed against one another.
The housing can advantageously be manufactured from plastic by injection molding. An injection-molded housing allows the shape of the housing to be adapted in a particularly simple manner to different designs of the housing of the throttle body through the design of the injection mold. Moreover, the requisite functional elements of the actuator can be integrated into the housing in a particularly simple manner during the production of the latter. For this purpose, the functional elements are first of all placed in the injection mold. The functional elements are then sealed off from the injection mold at the points at which they are not to be surrounded by plastic, and the injection mold is then filled with plastic. In addition, further elements of the throttle body, such as bearings, electrical connections or the like, can also be inserted in or mounted on the plastic housing of the throttle body. This results in efficient production, especially in the series production of such throttle bodies since the outlay on the production and assembly of the throttle body can be particularly low in this case. To avoid electrical short circuits, an electrically nonconductive plastic should be provided for the production of the housing.
It is advantageous if the stub pipe is integrated into the housing of the throttle body. It is then not necessary to manufacture the plastic housing with tolerances at the points envisaged for joining the throttle body to the stub pipe. Moreover, there is also no need for a manufacturing process specifically designed for high accuracy of fit of the stub pipe if the housing automatically leads to the functional element of the actuator being joined to the stub pipe. As a result, the outlay for the production of the plastic housing is particularly low.
It is advantageous if the actuator is designed as an electric motor. An electric motor has a particularly low susceptibility to faults and is therefore particularly suitable for use in a throttle body.
It is advantageous if the actuator designed as an electric motor is a direct-current motor, also referred to by those skilled in the art as a DC motor. In this case, at least the return body of the electric motor is arranged in the plastic housing of the throttle body. For this purpose, one or more of these return bodies can be placed in the injection mold before the injection molding of the plastic housing and can be enclosed or encapsulated with plastic. As an alternative, however, it is also possible to provide for introduction of the return body into the housing of the throttle body at a later stage. By integrating functional elements into the plastic housing, it is possible to reduce to a particularly low level the number of components to be assembled in the case of electric motors with many poles. The throttle body has a particularly small number of components to be assembled if, as is advantageous, the return body is constructed in one piece as a so-called pole tube.
It is advantageous if the functional element of the actuator, which is connected in a thermally conductive manner to the stub pipe, is the pole tube of the electric motor. The pole tube, which is arranged in the outer region of the electric motor, is particularly suitable as a heat conductor since it surrounds the heat-generating functional elements of the actuator, such as the rotor. The pole tube is furthermore a functional element of the actuator that can be reached particularly easily from outside the actuator.
It is advantageous if the magnet shells of the electric motor designed as a direct-current motor are arranged at least partially in the plastic housing of the throttle body. If production of the plastic housing by injection molding is envisaged, it is also possible for the permanently magnetic magnet shells to be placed in the injection mold for the housing before the mold is filled, thus allowing the permanently magnetic magnet shells to be integrated into the plastic housing as further functional elements. As an alternative, however, insertion of the magnet shells into the housing of the throttle body at a later stage can also be envisaged. Insertion of the return bodies and of the magnet shells into the injection mold can be automated, allowing sources of error that cannot be excluded with manual assembly to be avoided by machine-based manufacture.
When integrating the permanently magnetic magnet shells into the plastic housing, these can furthermore be completely enclosed by plastic. The enclosure of the magnet shells is not restricted to the ends and longitudinal sides but also includes the area of the circumferential surface of the magnet shells. This is particularly to be recommended when the housing of the throttle body is produced by injection molding. By virtue of this configuration, the plastic housing acts as a holder for the magnet shells, reliably preventing fragments of the magnet shells from detaching themselves. Magnet shells are often extremely brittle and normally tend to crack, favoring the detachment of fragments. A fragment detached from a magnet shell can cause a magnetic short circuit which, in turn, causes a reduction in the maximum torque that can be produced. Moreover, a detached fragment can cause mechanical jamming of the motor.
It is advantageous if the housing of the throttle body has holding elements for holding the magnet shells. This makes it a particularly simple matter to insert the magnet shells into the plastic housing after the production of the latter since the spaces provided for the magnet shells are clearly defined by the holding elements. The holding elements are designed in such a way that they ensure adequate retention of the magnet shells on the plastic housing in a particularly reliable manner. It is advantageous here if the holding elements are webs and/or springs produced in one piece with the plastic housing. As an alternative or in addition, it is furthermore also possible for spring elements, such as clips, which can either be formed in one piece with the housing or supplied separately, to be provided as holding elements for holding the magnet shells.
As an alternative to the use of a direct-current motor, as described above, it is advantageous if the electric motor is designed as a so-called electronically commutated electric motor, also referred to by those skilled in the art as an EC motor. In this electronically commutated electric motor, the windings that form the stator are integrated into the plastic housing. The rotor carries the return body and the magnet shells. An electronically commutated electric motor normally has a particularly high torque owing to the particularly close proximity of the rotor and the stator. Moreover, given a controlled supply of power to the windings of the rotor, control of the speed of the electronically commutated electric motor is particularly precise.
Both the direct-current motor and the electronically commutated electric motor can be designed as internal-rotor or external-rotor motors. Depending on the type of power supply, the actuator, in particular the electric motor or an electromagnet, is operated on direct current or alternating current.
It is advantageous if the actuator of the throttle body is provided for the purpose of moving the throttle butterfly as a function of a setpoint input for the power output of the internal combustion engine. By means of this embodiment of the throttle body, the heat generated in the actuator can be dissipated during the operation of the throttle body via the air flowing to the combustion point of the fuel.
The advantages achieved by means of the invention consist, in particular, in that the production and assembly of the throttle body are reduced to a particularly low level by virtue of the integration of a number of functional elements of the actuator into the plastic housing. In this arrangement, the stub pipe and a functional element of the actuator can be arranged in a fixed position relative to one another by means of form-locking joints, as a result of which the amount of space required for the arrangement of these two parts relative to one another is particularly low. Producing the plastic housing by injection molding allows the heat-conducting element and a number of functional elements to be embedded in the housing, thereby ensuring that the time required for assembly of the throttle body is particularly short. In this arrangement, the housing can have a number of recesses, into which moving elements of the throttle body can be inserted with an accurate fit, making the work required for assembly particularly simple. During the operation of the throttle body, the heat generated in the actuator can moreover be dissipated in a particularly reliable manner via the stub pipe, which is connected in a heat-conducting manner to the throttle butterfly of the throttle body. Since the throttle butterfly is here provided for the purpose of controlling the supply of a fluid, the heat generated in the actuator can be dissipated from the throttle body by the fluid.